Assessment of Fire Engineering Design Correlations Used to Describe the Geometry and Thermal Characteristics of Externally Venting Flames

Externally venting flames (EVF) may emerge through openings in fullydeveloped under-ventilated compartment fires, significantly increasing the risk of firespreading to higher floors or adjacent buildings. Several fire engineering correlationshave been developed, aiming to describe the main characteristics of EVF that affectthe fire safety design aspects of a building, such as EVF geometry, EVF centrelinetemperature and EVF-induced heat flux to the fac ̧ ade elements. This work is moti-vated by recent literature reports suggesting that existing correlations, proposed infire safety design guidelines (e.g. Eurocodes), cannot describe with sufficient accuracythe characteristics of EVF under realistic fire conditions. In this context, a wide rangeof EVF correlations are comparatively assessed and evaluated. Quantification of theirpredictive capabilities is achieved by means of comparison with measurementsobtained in 30 different large-scale compartment-fac ̧ ade fire experiments, covering abroad range of heat release rates (2.8 MW to 10.3 MW), ventilation factor values(2.6 m5/2to 11.53 m5/2) and ventilation conditions (no forced draught, forceddraught). A detailed analysis of the obtained results and the respective errors corrob-orates the fact that many correlations significantly under-predict critical physicalparameters, thus resulting in reduced (non-conservative) fire safety levels. The effectof commonly used assumptions (e.g. EVF envelope shape or model parameters forconvective and radiative heat transfer calculations) on the accuracy of the predictedvalues is determined, aiming to highlight the potential to improve the fire engineeringdesign correlations currently availabl

Geometrical characteristics of externally venting flames: Assessment of fire engineering design correlations using medium-scale compartment-façade fire tests

In a fully developed under-ventilated compartment fire, flames may spill out of external openings (e.g. windows); Externally Venting Flames (EVF) pose a significant risk of fire spreading to adjacent floors or buildings. The main aim of this work is to comparatively assess a range of fire engineering design correlations used to describe the external dimensions of the EVF envelope. The predictive accuracy of each correlation is evaluated through comparison with experimental data obtained in a medium-scale compartment-façade fire facility, using typical fire loads suggested in the Eurocode. A series of fire tests is performed, employing a ¼ scale model of the ISO 9705 room, equipped with an additional extended façade. An “expendable” fuel source (n-hexane) is utilized to effectively simulate realistic building fire conditions. An extensive sensor network is used to monitor the dynamic behaviour of a broad range of important EVF physical parameters and a dedicated image processing tool is developed to allow estimation of the EVF envelope main dimensions (e.g. height, width, projection). Digital camera imaging is used to determine the main geometrical characteristics of the EVF envelope. Comparison of fire engineering design correlation predictions with experimental data reveals that correlations for the estimation of EVF height err on the safe side in under-ventilated fire conditions; decreasing the fire load results in under-prediction of EVF height and projection. It is shown that EVF projection and width strongly depend on both excess heat release rate and height. In addition, the necessity to derive appropriate criteria for the identification of the EVF projection is demonstrated. The obtained extensive set of experimental data, covering three different fire load levels, can be also used to validate numerical simulation tools or evaluate the accuracy of other available fire design correlations

Fire safety aspects of PCM-enhanced gypsum plasterboards: An experimental and numerical investigation

New trends in building energy efficiency include thermal storage in building elements that can be achieved via the incorporation of Phase Change Materials (PCM). Gypsum plasterboards enhanced with micro-encapsulated paraffin-based PCM have recently become commercially available. This work aims to shed light on the fire safety aspects of using such innovative building materials, by means of an extensive experimental and numerical simulation study. The main thermo-physical properties and the fire behaviour of PCM-enhanced plasterboards are investigated, using a variety of methods (i.e. thermo-gravimetric analysis, differential scanning calorimetry, cone calorimeter, scanning electron microscopy). It is demonstrated that in the high temperature environment developing during a fire, the PCM paraffins evaporate and escape through the failed encapsulation shells and the gypsum plasterboard's porous structure, emerging in the fire region, where they ignite increasing the effective fire load. The experimental data are used to develop a numerical model that accurately describes the fire behaviour of PCM-enhanced gypsum plasterboards. The model is implemented in a Computational Fluid Dynamics (CFD) code and is validated against cone calorimeter test results. CFD simulations are used to demonstrate that the use of paraffin-based PCM-enhanced construction materials may, in case the micro-encapsulation shells fail, adversely affect the fire safety characteristics of a building. © 2015 Elsevier Ltd. All rights reserved